Firearms glossary

Common terms used in classifieds and gun-law summaries on Gun Sales Online, in plain English.

Action: The mechanism that loads, fires and ejects rounds. Common types: bolt, lever, pump, semi-automatic, single-shot, break-action.
Caliber / Calibre: The diameter of the bullet (e.g. .308, 9mm). The same caliber can have many cartridge types (e.g. .308 Win vs 7.62x51 NATO).
Gauge: Used for shotguns instead of caliber. Lower number = larger bore (12 gauge is bigger than 20 gauge). The .410 is the odd one out — it's a caliber.
Cartridge: The complete round of ammunition: case + primer + powder + bullet.
Magazine: The part that holds ammunition feeding into the action. May be detachable (most semi-autos) or fixed.
FFL: In the US, a Federal Firearms License — held by dealers, manufacturers and importers. Most interstate transfers must go through an FFL.
NFA: In the US, the National Firearms Act — covers suppressors, short-barrelled rifles, machine guns and similar items requiring extra paperwork and a $200 tax stamp.
Suppressor: Reduces the noise of a firing shot. Legal in most US states with NFA paperwork; banned or strictly limited in many other countries.
Semi-automatic: Fires one round per trigger pull and automatically loads the next round. NOT the same as “automatic”.
Bolt-action: Shooter manually cycles the bolt to chamber each round. Common on hunting rifles for accuracy and reliability.
Pump-action: Shooter cycles a sliding fore-end (the “pump”) to chamber the next round. Common on shotguns.
Lever-action: Cycled by a lever under the trigger guard. Classic Western rifle action; still popular for hunting.
Revolver: A handgun with a rotating cylinder of chambers. Either single-action or double-action.
Single-action: The hammer must be cocked manually before each shot.
Double-action: Pulling the trigger both cocks and releases the hammer. DA/SA pistols can do both.
Striker-fired: Like a Glock — instead of a hammer, an internal striker hits the firing pin. Generally lighter trigger than DA.
Centerfire: Cartridges with the primer in the centre of the case base. Most pistol and rifle ammo.
Rimfire: Cartridges where the primer is in the rim of the case (e.g. .22 LR). Cheap, low-recoil, can't be reloaded.
C&R: Curio & Relic — a US FFL Type 03 lets collectors buy older firearms (50+ years) directly without a transfer dealer.
Transfer: Moving ownership of a firearm from one person to another. In most countries, this must go through a licensed dealer with paperwork.